void mainImage(out vec4 fragColor,in vec2 fragCoord){
    vec2 uv=fragCoord/iResolution.xy;

    uv =(uv-0.5)*2.;
    // TODO: 这个地方还是不太了解
    uv.x*=iResolution.x/iResolution.y;
    float d = length(uv);
    // d -=0.5;
    float c = .25/d;
     c = pow(c,1.3);
    fragColor=vec4(vec3(c),1.);
  
}
float sdCircle(vec2 p ,float r){
    return length(p) - r;
}